


Fireproof

by JellyFicsnFucks



Category: Undertale (Video Game)
Genre: Aftercare, Break Up, Breeding, Cockblocking, Consensual Sex, Dirty Talk, Drug-Induced Sex, Embarrassment, First Time Blow Jobs, First Time Sex, Future Pregnancy, Getting Back Together, Hot Sex, Interspecies Relationship(s), Kissing, LITERALLY, M/M, Mating Cycles/In Heat, Orgasm Delay/Denial, Painful Sex, Semi-Public Sex, Temperature Play, Tranquilizers, Unrealistic Sex, Unsafe Sex, Vaginal Fingering, interupted sex, no one comes, thigh fucking, watched sex, worried about partner
Language: English
Status: Completed
Published: 2020-03-31
Updated: 2020-10-25
Packaged: 2021-02-28 21:40:00
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 5
Words: 14,318
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23413951
Author URL: https://archiveofourown.org/users/JellyFicsnFucks/pseuds/JellyFicsnFucks
Summary: Sansby is a pair that literally shouldn't work.Grillby is made of fire.Sans is 1 point away from dusting.How can this couple ever expect to have an intimate relationship?
Relationships: Grillby/Sans (Undertale)
Comments: 10
Kudos: 65





	1. Intercourse

In this room there is Sans. Only Sans. He tells himself.

Grillby gulps audibly. It’s hard not to be nervous as he stares down at the bare skeleton. Milky white bones spread out on the matress, waiting for Grillby to get closer. “I love you Sans…”

This was all for him. No one else got to see this lewd sight but him. Yep. He just had to keep telling himself that and maybe it might be true.

“I love you too Grillby.” Whispers are spoken to him. Too low to be heard by anyone else. It's the quiet and shy voice of his beloved. Sans reaches up with those special gloves and holds his face between both his hands. “I’m yours… All yours. Please don’t look at them. Only me.”

The flamester nods, words failing him. His mouth felt so dry. He wanted to reach down and kiss Sans. He was so damn close. So fucking close he could smell the soap he’d washed with just an hour before. But he can’t do it.

Sans lies back down underneath him, shirtless, pantsless… Everything is bare except for those damn gloves he has to wear. Without any of his clothes, especially his bulky sweater, Sans looked so tiny and fragile.

More so than usual.

Each rib looked soft and unprotected. Like a ceramic piece of a teacup, Grillby bet he could snap one of those bones accidentally with just the palm of his hand. And that was a terrifying thought.

When he reaches for Sans’s hips, he is surprised by the sturdy feeling. But still he holds him delicately like a small firefly. Cupping his hands so that the flames of his palms dont scorch the bone beneath. He’s careful not to touch for too long. He’s thankful when Sans’s gloved hands reach around and latch onto his shoulders, helping himself to hover over Grillby’s lap.

The two share a glance. Just beneath them their sexes are completely lined up. Grillby’s literal hot rod is standing erect and excited against his thigh. Sans’s wet entrance is dripping… small sizzles puncture the space between them. It sounds like cooking bacon and Sans doesn't want to admit he’s more hungry than he is aroused. But the drug in his body is making him wet anyhow.

“My body is ready for you.” Sans lets out a sympathetic smile at Grillby. “I know this isnt the ideal love nest for us, but we’ll manage, right?” It’s hard to take Sans seriously when he has his eyes set on the hot throbbing cock the walking furnace has. It measures longer than his pelvis and he worries it might reach the bottom of his ribcage. He looks down between them. “You, want to try putting it in?”

Grillby gulps.

Hell fucking yeah he wanted to put it in. Three years of dating and he and Sans hadn’t so much as shared a kiss. This painful knot in his stomach was desperate to pre just at the thought of holding Sans in his arms. But that was forbidden.

“T… tell me if it hurts at all.” He shudders to think Sans might lie to him because this was their only chance. There was a lot of pressure on this moment. He can feel the many eyes of scientists piercing down his neck as he bends Sans back and taps his spine so the skeleton knows to arch up at the touch.

He watches Sans expression thoughtfully, looking for any sign of pain or burn from when they touch but just like the doctor said, there wasn't any when touch was brief. He breathes a sigh of relief still unsure if they could go through with this. The steam of his breath comes out in the cold room. Everything has been iced solid to prepare for them.

They both gulp in unison. They’d been together for so long… now that it came down to this they were having performance anxiety. Literal performance anxiety… as half a dozen medical students looked at their coupling from beyond the glass wall.

Grillby grit his teeth, trying to keep his focus on Sans and not the giggling university students just a few meters away. “...Let..Lets try stretching you a bit, first.” Grillby sucks in a breath, trying to ease his nerves down.

Gently he taps at Sans’s legs, asking silently for the skeleton to spread his femurs nice and wide. He’s met with no resistance at all. Sans’s pants are heavily laden with the drug from earlier, even if his mind is clear his whole body shakes with lust.

That dripping pussy is just twitching to be fucked. Grillby’s face glows red with embarrassment. He’d never really gotten a chance to stare at his boyfriends unique ecto anatomy. And now half the science department were looking too. He wanted to growl at them beyond the wall to stake his dominance, but gloved hands touch his cheek again.

“Ignore them.” Sans begs. His half lidded eyes reach for grillby’s hand, careful to grab him where the insulating gloves kept them safe. He guides the hand up to his crotch. “Just a little more...and I’ll be yours.”

Grillby gulps again, but this time he cant taste bile. His lunch of woodchips and coals was coming back up. His stomach was too nervous for this. Maybe he couldn't do this after all. Maybe they should reschedule this mating day.

Sure, Sans’s legs are already spread for him. And … he can see the slick juices dripping from his entrance. His own cock is twitching in need, not from arousal but from the same drugs that are making his body tightfully pent up and desperate for stimulation.

“Okay… I’ll…” Grillby bends over his little lover. “I’ll put my fingers here?” He rubs a thumb and fore finger over the outside of Sans’s folds, and with a Y spreads open the lips. A beautiful azure flower sleeps beneath. It reveals the small entrance that is twitching for something to enter. Grillby’s finger slips in easily, practically pulled in. And to reward him, the most beautiful hiccup of sound erupts from Sans’s parted mouth. Like a surprise he hadn’t expected, the bundle of nerves in his pelvis are brushed up against the hot invading force.

Grillby holds his breath. Careful. Watchful. He stops moving until Sans gives him a small nod to continue. Sans’s flushed face, shivering in the cold and shivering from the over sensitive effect of the drugs, is wrecked before Grillby has even started. The skeleton has beads of tears at the sides of his eyesockets. “Please… keep going.” Sans’s mouth twitches. “I want it. I need your c-cock next. Please hurry~♥.”

Hot steam rises from Grillby, and if he didn’t already, he knows he’s fucked when the overhead speaker comes on in full blast. “LOWER THE TEMPERATURE.” Grillby and Sans wince as the microphones screech interrupts them.

“It doesn't hurt.” Sans is quick to tell them both. He shivers on the bed. “I like your warmth.” He whispers. His hands snake down over his thighs and towards the lips of his pussy, he spreads them open with his own hands and arches strangely for Grillby to keep going. “Please. Please… keep going.” He begs.

At this point, Grillby’s not sure if it's the drug talking or his lover… but he can’t give in like he wants to and fuck Sans’s sopping wet entrance.

That warning was there for a reason. If he doesn't calm himself, he might just end up using Sans up for his own grating pleasure. His temperature might get hot enough to scald or hurt Sans! And then what will happen? He’d be making love to a pile of dust and that picture didn’t help his boner at all.

His body doesn't feel like his own right now. He’s scared of hurting Sans. More than that, he’s scared of this intimacy between two monsters. Pornographies made it look so easy… when it was his turn to do it… Grillby felt a sweat roll down his neck. He tried to lower his internal temperature with slow uneven breaths.

He pushed his finger in, watching Sans squirm with the sensation rubbing against his inner walls. Grillby could feel ever bump and muscle squeezing around just the tip of his finger. He salivated at the thought of what that constricting heat would feel like around his cock.

Sans was so wet right now, he could easily take another finger. He swished the digits around inside of Sans’s hole. Hearing the sizzle die out when his fingers were fully doused in slick ecto fluids. He spread his fingers like a V inside of Sans, making the skeleton cry out with quiet gasps and a face that contorted to an O every time Grillby’s fingers hit the back wall of his magic.

“That feels so good…” Sans whimpers into his shoulder, still holding himself open for Grillby to play. The rough tactile feel of the heat resistance gloves hurt like sandpaper across his sensitive lower regions but Sans held open the gates of heaven for his love. “Please- put it inside.” Sans’s hips buckle into his fingers. Trying to get more and more friction out of the slender digits probing him. “I’m ready. I’m ready. Stars. Grillb. Breed me please. ”

That sets Grillby off in a huge way. The plume of smoke from his head ignites, even though the room is kept below freezing. He bends forward, putting his weight on one arm as he hovers over Sans’s splayed out body. His fingers start to speed through each thrusts, quickly setting the pace for something bigger as Sans moans and rolls with each jerky forward all the way until he’s wrist deep into that waiting heat and-

“LOWER THE TEMPERATURE!” The two wilt at the sharp sound.

“Thats the second warning.” Grillby seethes. Sans sighs with a disappointed whine.

Slowly he feels the fingers inside of him pull all the way out. Leaving him feeling empty and cold again. He closes his legs to keep his modesty and hands part of the blankets to Grilby to cover up. The flame monster growls as he covers his lap and sags forward on the edge of the bed. Sans drapes it over his shoulders and hides away his whole body. In unison, they worm away from each other to the farthest reach on the bed.

The two cast a glance up at the med students in the window. Painfully aware of the clipboards and stares. Sans grabs a pillow and covers his face wilting into the fluff. Grillby isnt as flustered if they stare at him naked. His chest ripples with flickers of fire, and he runs a finger through his head to smooth down the wisps of flame that formed his hair.

He tilts his head to the side and meditates a bit, even though he’s frustrated and pent up. He does his best to lower the temperature of his flame… if only a little.

Sans shivers in the cold. Even with the blankets around his shoulders he couldn’t keep out the chill. He really wished Grillby would come be back to warm him up.

The isolated room has been blowing iced air from Snowdin to keep Grillby from getting too warm. The flame monster’s natural fire had a way of hurting others when he least intended it too. And Sans was a helpless 1 hit monster. Small enough to crush under a fist and easy to dust to any type of magic. That’s why they had to take these precautions.

“Grillbz… Sans mumbles into the pillow. “I want to hold your hand.” Without looking up from his pillow prrotection he reaches his hand over underneath the covers. His reach isn’t long enough to tap Grillby, but he feels the warmth of him. The flame filled fignertips reach out to meet him the other half of the way. They wrap around the heat proof gloves and the he feels the disconnected tactile touch of his lover taking his hand.

“When we have kids…” Grillby stops, his voice catches with that faint tremor of fear that comes from wondering about the future. “Do you think they’ll be like you? … or me?”

“Hybrid hopefully. I want to pick them up.”

“... me too.” Grillby’s thick sigh fills the frigid air with hot steam. “And I want to pick you up too. ”

Sans flushes bright with blue across all his cheeks. When he looks up from the pillow the first thing he sees is the large window with so many people standing around observing their lifesigns and the readings of countless machines. He snuffs his head back down into the pillow. Even though he’d told Grillby so easily to ignore their onlooking stares, Sans was really having a hard time under the scrutinizing gaze.

The drugs in his system weren’t much help either. They were supposed to help ease copulation along… make every contact hyper sensitive. The doctors said it would take less ‘enthusiasm’ for them both to be coming if the job was half done. At least that was the logic of it.

This whole facility was built to help monsters like them help repopulate the underground. The problem was… monster’s came in all sorts of shapes and sizes. The variety of problems that sprang up from couples meeting up in the underground was deep and complex.

For certain monsters, their relationships were often forbidden and forced to comply with harsh restrictions. A monster with 1hp and a monster entirely made of fire, were subjects to those same restrictions necessary for their very health.

It was for this reason that icy air conditioners blew in the blizzards of Snowdin into their small frigid room. It was the same reason med students were watching them from that window above this studio. It was the same reason Sans wore these heat retardant gloves, and that infrared cameras kept measure of their body heat. It was the same reason this session was being recorded by the tiny red blip of light blinking at them from the ceiling. It was the same reason fire extinguishers and drugs and tranquilizing darts were aimed and ready to fire if the need was necessary.

Sans could break. Grillby could break him.


	2. Insatiable

“--V I TA L S A R E N O R M A L. YOU CAN CONTINUE IN THREE MINUTES.--” The loudspeakers make both monsters flinch. Grillby releases a sigh and his meditation pauses. 

Sans sighs too. For different reasons. 

In the thick of their passion, Sans was able to ignore the stares... but with the unexpected recess in the middle of their lovemaking, he can’t help but be hyper-aware of them. He tries his best not to look up again and meet the hungry sets of eyes peering down at them like lab animals. 

Just barely lifting his head, he follows the tresses of blankets to look at Grillby. 

His boyfriend looked exhausted and aggravated, and they haven't even begun. His usual orange-red pigment is reduced to a meager yellow. The flicker of his flames are weaker, which should be good for Sans… but he can’t help but think it's unnatural to see his partner this way. 

Sans wondered what Grillby looked like with no flame at all. Black like coals?

Like a matchbox burnt down to its very bottom? Would he be hurt? 

Would the fire monster lose every single health point if that fire went out? 

Grillby and him never really spoke about that, but the medical examiner assured them it would be fine. Plenty of elementals had 'done the dirty' in these halls… and Grillby was just another routine monster. 

Sans on the other hand… was new. 

Some scientists had built new devices specifically around his -ehm- 'limitations’. What they built for him was the stuff out of nightmares. There were horrific bulky prototypes of batteries hooked up to the soul of a monster to prevent it from dusting. Another device would constantly pump healing magic into his soul, so that any damage would constantly be replenished. 

The model they showed Sans looked like an over swollen trash bag filled with mud. Sans was repulsed by those options. A little fearful too. They were all experimental and had no guarantee to work. 

Grillby reassured him he didn’t have to choose any. 

But now Sans regrets not having those backup options. He didn’t want to admit it… but Grillby had already left sharp smolders of char along his body. 

“-- S I G N S A R E L O O K I N G G O O D, YOU MAY CONTINUE.--” Sans and Grillby recoil every occasion the speaker comes to life with its ungodly screech. They’d been waiting for that authority to continue with their lovemaking, but now they stare at each other with a blank face of a flounder fish. 

The heat of passion, tension, excitement, and romance once swelling in the air was gone because of their forced stop. Neither of them were in the mood anymore, even though the drugs were still affecting them. 

Sans drops his shoulders. He’s still stretched a bit… even if that heat between his legs has calmed and died down. “I’m um… good to go.” He's too shy to think of a better word for sex. It's his first time with Grillby and the cockblocking scientists have drained them both of their excitement. 

But he still wants to recover the mood. He clears his throat, cheeks burning with embarrassment as he whispers to Grillby. “Can I um… do you?” He nudges his head to nod down at Grillby’s pride. The glowing organ between the sheets. Grillby recoils a bit. 

“Oh. um... Can you?” The question isn't really for Sans but the doctors observing this above. He crooks his neck over to the window to await the answer. 

Thankfully, this time, a scientist doesn't use the cursed speakers and instead gives a thumbs up. 

Grillby swallows a lump in his throat, looking back at Sans to tell him the news since his small lover won't lookup. “They say yes." Grillby gulps. "But um... only if it's okay with you.” 

“Yeah. I wanna try. ” Sans nods his head, he attempts to rekindle that lost feeling of lust in his bones. He clears his throat of his initial shyness and tries to get the mood going again. 

He bends forward like a cat on the prowl, bending forward until he’s on his hands and knees. He can feel his pelvis exposed to the cool air.

\- exposed to anyone who wants to stare. 

But Grillby’s are the only eyes he cares about. He can see the flamester glowing a bit redder at the sight of his vertebrae and ecto butt wiggling in his view. “Ya gonna show me a good time Grillbz?” He purrs each word out with a sensual tip of voice. “Or am I gonna have to -do- it -all -myself?” Humming with a seductive tone, he bends down until his head is in front of Grillby’s lap. His blue tongue hangs out the tip of his mouth. 

He'd never seen Sans's ecto parts before. 

Grillby gulps hard. He didn't even think Sans had a tongue. Truth be told, he thought the skeleton might try to swallow him up the same mysterious way he swallowed burgers and fries. Disappearing into a magic void somewhere before his throat and mouth.

Today was raising a whole bunch of new challenges for them both. But now that an azure-blue tongue is peeking out from his teeth, Grillby shudders with the awareness of where that sinful mouth was going. His flaccid length starts to get worked up again. 

With his teeth pressed together, Sans takes a bite of the bed sheet between them, lifting it to reveal Grillby’s glowing holy flame sword. Sans's eyes light up. It looks so much bigger from this close. He can literally smell the heat rolling off Grillby. It's sweeter than a bbq and musky with Grillby's unique scent. 

He hesitates a bit. Like the rest of Grillby, his hot rod is... well ... hot. 

The meager yellow flame was still pure elemental fire. Sans wasn't sure how exactly to put it in his mouth. Cautiously he tips forward. Unsure what to expect as he leans forward to drag his small blue tongue flat against the underside of the thick shaft. He flinches before he even makes contact, but he's not hurt. 

It tastes like magma. Like sucking on the salt of a hot stone on a Summer's day. The earthy taste of minerals. He can hear Grillby curse as his tongue sizzles across the arch of his length. The flame doesn't weaken though, it gets even stronger. 

“Shit Sans…” Grillby bites at his hand to cover the noise he makes. Sans smirks. Apparently, that felt good to the elemental. But Grillby is taking slow and painful long breaths again, like when he'd tried to meditate earlier to lower his flame. 

He's trying to control himself... 

...and Sans sucks in his teeth wondering if this was hard for him. The burning flame was his boyfriend's entire body... surely weakening it didn't feel good. “Nngh-!” Or did it? 

Sans laps again at the peak of the mountain. Finding a burnt orange goo of magic budding at its tip. Despite it being a liquid, the substance bubbled out from his cock without dousing his flames. 

Sans was greedy enough to lick it up though. The raw volcanic explosion would soon be inside him... and Sans couldn't help but be curious about what it might taste like. There's a particularly strong moan when Sans flicks his tongue again and swallows. Grillby's hands caress at his shoulders briefly. He wants to hold Sans. But his nervous digits recoil. He holds a hand to cover his mouth. 

Sans wraps his tongue around the thick flame’s hot rod. Inside of his mouth, it feels like he’s lapped up a hot sausage straight out the pan. He closes his eyes and tries to suckle down the shaft, ignoring the sharp heat only because Grillby looks like he’s enjoying it so much. 

His member has stood back up, erect, and the monster’s mouth his parted open with a slight rasp of breath. Sans looks proud of his work. 

With every gulp, the wet of his tongue sizzles against the flames. It feels like pop rocks have scattered all over his tongue, causing tiny explosions. 

When the skeleton looks up, with cock still in his mouth, the top of his eyelights are shaped like hearts, pleading with his partner for more. Grillby looks taken back in more ways than one. “Fffuck sans.” Grillby huffs. His heat spikes up as he watches Sans try to swallow it all. Down to the base, Sans bobs his head up and down. 

It surprises Grillby when Sans starts to gag. He reaches out for Sans's head to push him away. But the sultry skeleton just hangs on. Riding through the motion until the back of his throat opens up. Tears in his eyes. He finally swallows Grillby all the way and gives a triumphant hum. 

The vibrations travel up his cock and Grillby shakes. "nnnh~" Breathing strained, Grillby makes small gasps as he watches the magnificent skeleton bob up and down, slick tongue working magic over his magic. 

Sans pulls away briefly only to open his mouth. Showing Grillby the burnt sienna colour on his blue tongue. “Tasshes guud.” Sans says with his tongue still out. He pants. The texture of precum is thick and savory. He keeps it on his tongue a minute longer, just surprised by the thick waves of steam forming in his mouth from the hot and cool air mixing. 

“Sanss.” Grillby cringed, breathless. "...Don't... swallow that." His light glows red, temperature spiking up as his partner ignores the warning and tries to swallow it all. 

"...yum♥"

The sultry skeleton bends down again to suckle up his dick. He challenges himself to take it deeper into his mouth. Like he did before. Wanting to earn Grillby's gratuitous moans. 

Little by little, his legs open wider. Allowing Sans to place his gloved hands on his thighs and press his face flush against Grillby's naval. Rocking forward with each slurp, Sans's saliva is the thing saving him from burning up. 

His boyfriend's hasty pants and moans encourage Sans to keep going on. Even as a burning intensity starts to fill Sans’s mouth. 

It eventually becomes too much. He sits back with a whimper, fanning his tongue with the palm of his hand. “Haawt hawt. hot.” His tongue out of his mouth to cool off. 

“Just… spit Sans!” Grillby’s face flusters into a simmer when the skeleton makes a loud gulp. Face burning with an intimate enthusiasm to continue, his little lover makes a small whimper. 

“... You burned yourself didn't’ you.” Grillby deadpan whispers. Sans shakes his head left and right, not trusting himself to say anything because his ecto tongue is too damaged to resummon. 

...So much for sweet-talking his way through this.

"Shit ... show me." Grillby, whispers. "Did you hurt yourself??" Sans whips his head back and forth quickly to assure him he's fine. But he is nevertheless ignored. Shudders wrack his body with the uncomfortable sensation of being CHECKED. It fills his soul in a way he can't deflect, and he knows Grillby must have read that he's hurt. His health isn't any lower, it definitely won't alert the med staff, but his tongue is roasted. 

Even still, Sans makes puppy eyes, pleading with Grillby to continue. He doesn't want the lab guys to find out about this slip-up. Even if they were watching, who knows how they would interpret that fucked up blowjob.

Grillby gulps. “You’re still good?”  
Sans nods his head again and again.  
“Okay… okay..." He doesn't feel good about letting his partner continue... but he was already so close. "...Lie back.” 

When his bare scapula touches the back of the freezing bedsheets a shiver runs up his spine. The ceiling is terrifying. Bright iridescent lamps illuminate the room in a white sterile glow. Large metal ventilation shafts cross overhead and there is a small turbine that spins as cool air blows into the room. A camera is pointed at them. The red light in the corner of the room continues to blink until Grillby eclipses it with his body. Now the fire monster cages him in on all sides and blocks out the ceiling lights with his own auburn glow. Sans sucks in a deep breath... 

Holy shit. This was happening. 

He spread his legs wide, wider than needed, for Grilby to come to straddle him. Those hot large hands touch his upper thighs. His legs settle just above Grillby's hip. The press of their sex together sends an aroused shudder through his frame. He looks at Grillby. 

Grillby looks at him. The tip of his head is sliding up against his folds. There's a sizzle of heat and wetness when the two organs meet for a brief hello~ and both monsters let out a small gasp at the new feeling. 

“--N O P E N E T R A T I O N P L E A S E--” The loudspeaker shrieks. 

Sans just about has a heart attack when the static-crackling monitor interrupts them yet again. He's in agony here! With a groan he yells back. “WHAT THE FUCK DO YOU MEAN!?” He slams his hand on the bed and twists on Grillbys lap to look at the window. 

It's a mistake to do that. 

He sees various med students and recognizes some faces among them. One of the bunny’s girls who were his neighbors was studying medicine here. Alphys was here. Fuck… even some of his old colleges in the labs were here… 

“PENETRATION IS ONLY ALLOWED DURING EJACULATION.” One of the monitors bends to speak into a microphone. From across the glass it looks like he’s just talking normally, but the speakers are cranked to 11 and the crackle of the audio makes it seem like he's yelling. Sans feels so tiny every time the speakers overwhelm him. “WE HAVE TO THINK ABOUT WHAT'S BEST TO KEEP BOTH MONSTERS AND FUTURE CHILDREN ALIVE. PENETRATION COULD BURN, OR TEAR, AND LOWER YOUR HEALTH.” 

Sans grit his teeth and sent glowered back at Grillby. This was his fault! His damn fire boyfriend couldn't help being so hot~but Sans had put up with a lot of shit to be his partner. To find out now, that sex was off the table forever… ???!

...He wanted to scream. Sans was so pent up and frustrated he felt like crying. Grillby saw the pout a mile away. Immediately he raises his hands in defense, trying to console Sans without that added layer of touch. 

“It's... it's not all bad Sansy... I mean… we both can still get off! And…” He leans forward a top Sans pressing the skeleton flat against the mattress again. Making sure his eyes are on no one but him. “I’ll make sure to take you to heaven~.”

Sans doubted that. It was hot as hell right now. And not in a sexy way. 

He was sweating and freezing at the same time. And Grillby’s sexy talk was pretty empty. What were they gonna do? Masturbate with each other? Come inside a funnel?? Sans didn’t think he could give head again any time soon. His ecto tongue still scorched even though it was unsummoned. 

But that didn’t stop Grillby from peppering his ribcage in small kisses. Trailing down from his collar bone down to his hips. Grillby’s tongue left little red scorches everywhere it went. Sans shivered with anticipation. 

Everything they’d been working too felt like it reset to zero. Sans felt dryer than the sands in Hotland. And the new bruises and burns were starting to sting now that he wasn't super horny. This would definitely hurt tomorrow. 

Instinctively Sans shimmied a hand down his own legs and rubbed his fingers into the wet heat rolling between them. It's not in the slightest way comfortable. He wanted to reclaim this sensual mood. But the fire retardant gloves he’d been given are rough around his sensitive ecto skin. He can’t feel anything through the rubber fingertips, vaguely knowing where his own good spots were. 

Grillby helped join him. Fingers entering with Sans’s own. “You don’t have to touch me.” Sans’s face is completely flushed blue. He looks up at Grillby with a gulp. “It’s not… um… going to do anything.” 

Yeah, he knew he didn’t have to stretch Sans out anymore. It's not like either of them would get a chance to use that space. But Grillby offered a small smile, “I want your first time to feel good.” Out of every other humiliation in this room, the least his partner should get is a full orgasm. He circles his clit in a small circle, making Sans seize a breath from pleasure and pain. He shakes his head wildly, no. No. No no. 

Compared to the fingering earlier, inside him, he was already heated and the extra warmth made him feel full… but the hot stimulation to his clit just made his whole body shake. It felt like a burn straight to the most sensitive part of him. He bit his jaw tight, trying not to whimper or make any displeasure sounds. If one of the observers saw his discomfort they’d pull the plug on the whole operation. 

“Y...you can use… nn.. Use my thighs.” Sans offers. He gups hard. “I'm sorry. This…” It hurts. He doesn't want to say it. Doesn't want the lab guys to make them stop. But it hurts every time Grillby lays a kiss to his chest. Small burns of flames litter his frame. It looks like hickeys. But leaves a scathing rash more painful than Sans will admit. 

He gets up, from the bed. Getting to his knees and turning around to show Grillby his hind side. His ass wiggles in the air and his knees knock together, creating a small thigh gap for Grillby to rub himself into. Sans looks back at him, arching his spine to look back at his partner. 

“You can… go faster too. Ya know?” He looks down at the mattress and mumbles so that only he and Grillby can hear. “I … I just want to get this over with.” 

Grillby clears his throat, trying not to take those words to heart. It wasn’t an insult at him. It was just their situation that was entirely shitty. “Okay…” He positions himself behind Sans again, briefly touching over his lower back to make Sans relax. The skeleton sags into the mattress, head down ass up. His fingers tightly gripped the sheets. Unsure of what it would feel like. Or when it would come. 

He can feel Grillby’s whole existence behind him. The flamester, lines himself up against his ecto thighs and pushes his penis between the chubby flesh. It's not as tight as a pussy. And Sans tries to pinch his legs closed to replicate that feeling for Grillby. But it's just not the same. 

“Is… is it good?” Sans whimpers into the mattress. For him, he feels nothing but the hot candle of burning wax between his legs. There's no stimulation at all, except for a small rocking motion as he’s bobbed gently forward.

“You’re wonderful.” Grillby lies through a hiss of steam. He risks grabbing Sans’s hips. Feeling awkward about his hand placement. He can see the small tremor Sans makes when the flat of his fingers make contact with the cool ecto jelly. “I’ll go faster… now? You still okay?” 

“Yes, I’m fine.” Sans winces. He can feel imprints of Grillby's hands scalding his sides. Like a brand. Oh fuck. He’s not sure if it will leave a mark or not, but his bones just want to jump out of his ecto skin and run. Instead, he makes small quick rocking motions along with Grillby’s thrusts. Helping to reach an end they both desperately want. 

Grillby starts to thrust a bit roughly against his thighs. Every now and then his girth slips past and plays with Sans’s slit. They both make a small moan at that sensation. His hands try to comfort him as he rubs up against Sans’s thighs. Caressing his hips and ass, doubly using them as a handhold to pull Sans back against him. 

The plump blue ecto flesh that formed between his legs was soft, Grillby tries to rub against it as much as he can. Creating slow friction starts to get them both in the mood again. 

Things are just starting to heat up again. Literally. 

Sans winces as his thighs scorch every time Grillby's rod passes them. The blue ecto color has started blistering a bit red. Grillby's hands start searing into his skin and Sans has to hide his cries as moans. He grips the bed sheets tightly. Just let him finish. Just let him finish. His whole body tenses as fire claims him. 

The speakers go off again. But they both try to ignore it. Grillby's thrusts are hurried, trying to get off and bring Sans to that same pleasure as they flounder about. 

Sans reaches behind himself, arm bent uncomfortably. He tries to grab for Grillby's hand. Fuck everything burns. Sans has never felt this hot before. He opens his mouth and pants for air. He needs some water. The sheets below him aren't even cold anymore. They just feel moist and sweaty with humidity. 

Grillby's hand reaches his own. Their fingers entwine. Fuck. He's here with him, right? Sans closes his eyes tightly. "I... i love you." Sans whimpers. His hands grip tightly with Grillbys. He feels the flame monster whisper the same words along the nape of his neck. Shit. Sans swore he'd been touched with a hot iron. He bit his teeth together, trying his best to be silent. 

The speaker goes off again. Sans flinches. Please. Oh stars. Just shut up for one godddamn minute and let them have this! Sans felt closer to the end. His body was so damn sensitive now that it was burning raw. Grillby's cock slides so easily through his legs, bumping past his clit to send tremors through his spine. 

A little more. A little more... and they'd both...

~~~  
"I don't think they're listening to the warnings anymore." One of the lab guys says. "Should I pull the plug?"

"What's the temperature readout?"

"43... and climbing." 

"Run a check on them both." 

"Kay... looks like... the elemental is down by 50% the skeleton... a few decimals have been shaved but it's flickering. Could be our equipment." 

"... Let's not risk it. Throw in the tranquilizers."  
~~~

Sans feels really woozy. Not sure if its heat stroke or fatigue... Grillby's slaps have taken alot out of him. Was he done yet? He winced into the mattress. His hips hurt. He felt Grillby suddenly catch on the outside of his pelvis. He winced again. Hoping. Pleading. Please come inside. He needed it. He had earned it!! But his head was so damn woozy... He shut his eyes tight ... 

...and when they opened he was sitting upright in a hospital bed. Dressed in a white robe and arm hooked up to a few different drips. He was bandaged and taped up in a lot of odd places. His soul was seperated from him. He felt an unnatural chill hollow throughout his chest. On the rolling desk next to him, his soul was contained in a small glass jar among some more IVs and wires. He tuts his teeth. Fuck. 

"Hey Sansy." Grillbz voice shines in like the sun parting through the clouds. Sans smiles to heart it, glad he wasnt alone. He turns his head a bit to the left. 

Grillby is in another bed beside him in the hospital room. He's not bandaged at all. Good. But his color has yet to return. He shines at a low spectrum of yellow flame. It looks sickly. 

"Am I pregnant?" Sans asks. And he sees the paleness on Grillby before he even answers. 

"The... the doctors were adamant to stop the mating ritual. They um... they said maybe we... are incompatible... for children. They tranquilized us and moved us here to check our vitals." 

"oh." Sans says. He doesn't even feel anything. Everything feels numb and painful. "...When can we try again?" 

"... I reserved a spot. It's for another month." 

"...oh." He wilts. This was a worthless attempt then? Sans drums a finger tip over his stomach. Nothing was there.


	3. Incompatable

There were certain rules about interspecies relationships in the under ground. Rock monsters were expected to meet rock monsters , whimsums with whimsums, dogs and dogs …and well. It worked nicely for most couples, like the previous king and queen. 

It was a way to keep their limited monster kind ‘pure’ but now and then there would arise couples that didn’t fit the standard. For these monsters, their relationships often met harsh restrictions.Criticism.

The underground was facing an underpopulation problem, monster breeds were becoming extinct. If a couple insisted on staying together, both monsters had to be tested to see if their magic was even compatible. The last thing the underground needed was more needless death. 

Breeding was only allowed under observation. And for a monster with 1hp and a monster entirely made of fire, those restrictions were necessary for their very health. 

… ‘Incompatible’ They said. 

Sans hisses a breath between his teeth. 

How could the doctors say they were incompatible?! He and Grillby got a 60% match last time! They passed these tests before! They followed procedure! They had reserved a room, endured the tortuous stares of scientists watching them fuck like animals in a cage! He was humiliated and unsatisfied, and even after all that~ he and Grillby were still unable to have sex. ...Maybe things got just a little bit out of hand but some assholes decided it was dangerous and they were tranquilized on the spot. 

It had been a week since that mishap. It was deemed to be such a failure, they had to be tested again. 

Sans kicks his legs back and forth from the high top chair. Meanwhile Grillby taps his feet impatiently against the tiles. The two of them wait in the doctor's office together. 

“...d-do you think…?” Dread seeped through Sans, almost as though a cold wet raindrop rolled down his spine. “Will we... match again?” The fear of it all made the small skeleton shake. Unlike Grillby, he wore nothing but a small white patient robe He’d been stuck in the hospital for the week, nursing burns.

“...” Grillby tries his best to be positive, but he just can't bring himself to say the words Sans wants to hear. His mind is solely on regulating his temperature. Now that Sans was sitting so close, he was sure his heat was bothering the tiny monster. It was one of his fears not to keep his heat in check. He can’t even imagine what torment his love endured during that embarrassing session. Sans still had scars across his bones. Fresh burns covered in ointment and wrapped in gauze. He did that. Some of them might even be permanent. And, if that was the case, he’d never forgive himself. 

The two of them wait in the tiny office. White wallpaper with small hearts decorate the outer wall. From the corners of the room are rows and rows of wires that have been twisted into submission to form some curly loops where several medical equipment and a television were plugged in. Currently none were on, but the expanse of tools made both monsters very uncomfortable in the doctors workspace. In the top right corner of the room there is a camera with a red flicker of light that tells them that this session is being recorded. It is something they both are eerily familiar with. Being watched. 

Grillby clears his throat, tired of the silence. “.. did… uh.. The soul sample… hurt?” He waggles a finger over his own chest in the shape of an x, as though he were showing the procedure to the monster already overly familiar with it. 

Unlike the first noninvasive tests, which were done by studying their magic attacks, the doctors took a shaving of Sans’s soul to see if it matched up with Grilbys. A small sample of soul wasn’t much to a normal monster. Grillby did this with nary a flinch. The medic was able to snip a piece off with a fine point tool. 1 hp was shaved off quickly. 

But when Sans had to do his…things were a little different. 

Grillby, Sans, even the doctor, took the soul sample in pure silence. Everyone was holding their breath when the doctor shaved off a small fragment of the soul. Fractions of what they usually used for testing. 

“It hurt a little… yeah.” Sans’s fists clenches the desk that he’s sitting on top of. He swings his legs out again. Unable to touch the floor. “But… I think we’ll match up. So … it's worth it.” 

“... Sans? …. What if we don't?”

“We’ll definitely match.” Sans bites his bottom lip.

“...You don't have fire magic and … I don't have good control of mine.” 

“We’ll definitely match.” Sans says again, staring at the ground. He’s shivering so much. 

It’s unclear whether it's from nerves or pain. It only started when the physician left the room that he was able to show his vulnerabilities and shake like a baby bones with Grillby. He knows Grillby wont hurt him. Won’t judge him. These procedures were taxing on a small skeleton. 

Grillby partially feels like he should leave. Regardless of what the test results say, he and Sans weren’t a match… this wouldnt work. Coming here was a mistake. Sans’s love and trust was something better put in another monster. Maybe there were other skeletons in the underground. Maybe in the city. Sans would be better off with one of his own. Repopulating his species was important. Besides they were an elemental and an undead, who knows what horrid children would come from their breeds mixing…

But Sans loves him. 

Even after being publicly humiliated in front of his previous co-workers, friends and neighbors who were also studying medicine, he still wanted to go through with being mated in front of them. Even after being burned, he still wanted to have his children. The monster was shaking, hoping the test results were positive so they could be together. 

Grillby feels like he doesn't deserve that love. … He hopes the results are negative. He hopes Sans will lose interest with him and even if it hurts him… he hopes Sans will find someone else to love. Someone who won't burn him. 

… 

He couldn't help but notice how small Sans looked without his usual jacket. The white robe only had a tie in the back, and left him quite exposed. His bare bones were covered in blisters and in some -more damaged areas- wrapped completely. Grillby clenched his hands into his lap. Fuck… if only he’d shown some restraint this wouldnt have…

“I’m hoping for a girl.” Sans whispers. He doesn't really stare at Grillby when he talks. He speaks low, down to the floorboards, where only his innermost desires can be said while he swings his legs back and forth. “I’ve always liked girl names better. They roll off the tongue. Like Arial. Or Lucida. …If it's a boy. Maybe Roman.” 

Grillby swallows hard. He’s not sure what to add to a conversation about made up children. He clears his throat. “... um… font names. Is that a uh? … thing for skeletons? Tradition?”

Sans brightens up just a bit, smiling as he talks about his family. “Yeah. I get my name from Comic Sans. And Papyrus… well heh… it's obvious once he opens his mouth. I used to have a dad long ago. I have a few memories. There’s really no record of him… but I know his name was WingDings. Since skeletons dont have lungs or breath like most monsters… our name creates our script. Our language. It's our identity. So it's important to choose a good one for kids.” Sans stops speaking suddenly and looks up at Grillby, face flustered. “Aaaa unless… you had some ideas for names too! I’m not set on a name or a-anything!!! If you have suggestions… I want to hear them too!” 

“...” Grillby takes in a deep breath, it fans his flames as he stares at the excited skeleton. San’s eyelights glow with this brightness that rivals his own fire. He loved seeing Sans look so happy. Hopeful. He was starting to think this whole charade was depressing him, but he’s glad Sans can get excited over something like this. Wanting to keep him this way, Grillby quickly tries to think of his own family tree.But his face sours as he realizes for perhaps the first time in his life the nameing scheme.“We all have fire pun names...” 

“Oh!!!” Sans shines. It’s been a while since he’s heard a good pun. “What are they?” 

“Hmm… yeah, you might like them.” Grillby chuckles. “My mother is Ignis. My father is Char. A cousin of mine is named Fuku Fire.” He reminisces about it with Sans. He hadn’t seen them in a while. Since he moved to Snowdin, his family has felt so far. Thinking about it now, it had been a long while since he’d seen another elemental.

“When I used to live in Hotland, almost all my neighbors were elementals. They had names like Ember and Heats Flameman. I remember a Pyro that used to play down the street with Sparky. I didn’t really think about it until I moved.”

“Heh… Those names are cute… I wouldn't mind naming them like that.” Sans’s smile is warm and genuine. Grillby feels his soul pounding just staring at the little twitch in his mouth. “ Fire names… how about….” He puts a finger to his chin, deep in thought for a pun typhoon that Grillby could only prepare for with a sigh and slacked shoulders. 

“Light.” Grillby visibly released a breath. That wasn't as bad as he thought. “If it's something-light, she can have a fire and font name. There's lots to choose from.” 

“... that sounds nice.” Grillby hums. He wants to hold Sans so bad. Talking about their future together… made a small fire burn in the pit of his stomach. He wasnt sure if it would work… but he wanted to give this a try. Quietly, he extends his hand to the other. He tries to lower his temperature. Lower. Lower… until his flame is a small brown of light from his fingertips to his elbow. 

Sans blinks, gulps at the offer.He lifts his hand with a tremble and holds Grillbys. 

Their fingers barely touch for a second but from the first touch Sans jumps back with a jolt of pain radiating up his arm. It was so much different than wearing gloves!

Grillby sighs and closes his eyes. “ ... I don't think ...this is going to work-us. It’s nice fantasizing about the future and all Sans… but … we can’t even hold hands. How are we supposed to start a family together? Maybe we should break-” He’s surprised when Sans takes his hand again. 

The sharp clasp makes a clap in the room. Grillby snaps his eyes open, looking at their hand and following the arm up to look at Sans. His jaw is clenched painfully.“Sans?!” He’s forcing himself to hold grillby’s palm with his own, slipping their digits between each other even as he burns up with the low flame. “Sans! Let go!” 

Sans shakes his head. “Sans! Don't be stubborn! Let go!!!” Grillby grimaces, he tries to pull his hand free but Sans is clinging to his palm. The only way he can separate them is by slapping Sans’s hand out of his. He slides off the examination table and places a huge distance between them. “You could have hurt yourself!” He yells. He stands away from the table and walks over to the opposite wall. 

“I didn't.” Sans mumbles, clearly lying. His hand trembles but he folds it into his lap like the pain of being burned isn't there. Even from this distance Grillby can see he’s hurt! He opens his maw to fight back, the sizzle of flame hot in his mouth- but just as he sucks in a breath to yell- 

-the doctor walks back in. 

She looks around the room. Obviously having walked in on some lovers spat she wasnt sure about. “Do you need another minute?” She meekly asks. 

Grillby snaps his jaw shut and shakes his head. Like a good patient, he takes a seat back on the examination table beside Sans, but this time he is actively making their distance a little farther than before. 

The doctor looks over her charts with the results and scoots a swivel chair a bit closer. “Lets see here. Grillby, your element is fire..” Grillby sunk his face into his hands. That should have been obvious from the flame swirling around his whole body. Sans even makes a small giggle. “Usually monsters of your type have a good handle of flame magic. You can probably change the air around you to increase or decrease the density of your flame as well as change the chemical composition of the air to change your flame color like your little cousin Fuku does. How old is Fuku by the way? I haven’t seen her since she was thiiiis high.” 

“She’s in highschool now.” Grillby groans. His apparent boredom and hatred for the conversation is unheard by the physician as she continues her analysis of his magic. 

“Well you have 0% body fat, your vision looks great, and there were no signs of heartburn. Oh-hoh-hoh!” She begins to laugh into her clipboard. Apparently this was the highlight of her week. Meanwhile, Grillby sinks his head further into his hands. He’s so glad when she shifts her attention to Sans. 

“Sans you have a strength in the wind element. I woulndt be surprised if you learned gravity magic one day!” The smile on Sans’s face slips off. Slowly the sinking feeling that this doctor was an idiot starts to become clear. Sans and Grillby collectively rolled their makeshift eyes. They didn’t come here to be lectured about their magic types or family history. They wanted to know about their match. 

“We weren't able to analyze most of your magic because of such a small sample… but it appears you might have some latent summoning abilities. If that’s true, that is a very rare ability you should be proud of. In the whole of monster history I think there have only been a handful that had that ability.” She pushes up her glasses. “Lets see here. According to your charts your calcium level is through the roof! Oh-hoh-ho!” 

Sans was going to strangle her. Where the heck was Alphys? Who the heck was this newbie? … She looked familiar too. Sans might have sworn she was one of the attendees in the glass window. He really didn’t want to imagine she was one of the people who saw that. 

He looks down at his hand. The burn from Grillby just now, still hurts. Not enough to sear the bone or cause a welt… just enough that it was sensitive to the air and throbbed in pain. If someone used healing magic now, it might feel better. But he also didn’t want to tell this current doctor about his condition. He didn't want to say anything. If for any reason a doctor thought their relationship might be dangerous they might deny them use of the facility entirely. 

“The good news is, you have an affinity of over 57%” It’s less than it was the first time. took the test. Sans pinches himself. “It's a little more than half. These are good numbers to have since a synchronization rate of 40 or more is needed. With this you should be clear once your injuries heal up.” 

Sans perks up in an instant, he thought it was over. “D-does that mean??” He looks over at Grillby with a sparkle in his eyes. 

“Yes, you can copulate under supervision.” 

Sans shook his arm. It startled Grillby in more ways than one. He immediately sagged away. “Grillby! Didn’t you hear? She said we’re compatible!!!” 

“... yeah. Yay.” Grillby tucked his arms close into himself. He eyed up at the scrupulous camera wired into the ceiling. “I’m glad..” He says it to the camera rather than his partner. The pinprick red light in the corner of the room is something he’s never going to get over. 

Grillby seethed inside. He tried to force a smile for Sans… His boyfriend was relieved at the news. They could be together! This was amazing. This was something to celebrate! 

But deep in his gut, Grillby felt the news was more a punishment than a reward. This wasn’t the news he was hoping for. He’d hoped it would give them bad news that they weren’t compatible. He hoped a doctor could break them up, because he’d never find a way to say those words to Sans himself. 

Because.. the fact was, even if they could be together…How was he supposed to be with Sans? If simply holding hands burned his partner, how were they supposed to be a couple? 

He hated being flame… he hated that Sans had 1 health. And every time Sans fidgeted or flinched Grillby would hold his breath in surprise, unsure if he’d actually made Sans fall down. 

It was just a matter of time with someone so fragile… 

Even healing had no effect once the burns settled in on his bone. His skeleton boyfriend was looking a lot like a mummy with all the tape around him. Grillby gulped. He didn’t want to hurt Sans anymore than he had. 

Small movements were fine. If Sans was fast, he could tap his arm and high five him. But it seemed whenever they tried for something longer the skeleton would suffer immediate burns. 

Hand holding, hugging...kissing… those easy things for couples were off limits. And yet somehow Sans talked him into having kids. Having sex. Or at least… trying to have sex. 

He should have said no. 

He couldnt imagine being at a funeral with Papyrus, explaining that his brother died because they fucked so hard Sans dusted! 

Grillby clenched his chest. His soul couldn't take much more of this. If he didn’t say something now he might regret it for the rest of his life. Or whatever short life he was going to end up giving Sans. 

“I don't think… we should do this again.” 

“Agreed!” Sans says all to quickly. To say he was shocked would be an understatement, Grillby feels something catch in his throat. A depression thats been there all along. 

They dont work together. 

“The safety measures weren’t enough.” Sans pouts. “The gloves worked great… but tranqing us was the worst thing that could have happened. We picked the 3 minimum safeties so why weren’t they used?” 

“A doctor assumed the risk and-” Grillby tunes it out. He had thought for sure Sans was about to break up with him. He wasn't sure whether to be relieved or concerned this wasn't the case. 

After the endless conversation with the, frankly useless, doctor they go home. 

It's the first time all week Sans has been dismissed. He leaves in a wheelchair. Sans promises it's just because the staff are over worried… 

Papyrus had come with some clothes and a scathing glare at Grillby. Which he deserves. 

It's a good thing Papyrus is here for Sans. He has something that Sans desperately needs, but Grillby can never give him. As soon as the two brothers see each other they hug. Bones clacking bones and Papyrus’s wide arms squeeze his brother tightly. A wide grin spreads across Sans’s face. 

Grillby keeps his distance. 

His partner looked so happy when he was talking to his bro. Hugging. Holding hands.When Sans starts crying, telling him about how they failed, Pap touches his shoulder and assures him it will be okay. Grillby feels his gut coil. 

Papyrus, Sans, and Grillby walk home to Snowdin from the Hotland Hospital. Well… roll home. Since Sans is stuck in a chair and Papyrus holds he handles to wheel him around. “Nn I can open a short cut-”

“NO” Papyrus rolls his eyes. “NONE OF YOUR TIME AND SPACE SHENANIGANS SANS!! YOU STILL HAVEN'T RECOVERED.”

The way is mostly filled with idle chatter. The bumpy roads of waterfall and the snowy dirge of Snowdin causes some problems for the wheels, but Papyrus pushes him over the obstacles with ease. They arrive at their home and Papyrus invites Grillby to stay with them for dinner. 

But on the front steps of Sans’s home Grillby has other words in mind to share with the skeleton. 

“...I..” Grillby clenches his fists by his sides. They dig deep down past the clothing, clenching at his thighs to pinch himself- to work up the nerve to say something thats been on his mind for months. “I don't think… we should see each other. Anymore.” Grillby’s throat feels parched for the first time in his life. Sans and Papyrus look at him with a strange stare. 

Were his words something alien to them? Did he have to say it clearer? “I don't care if the medical report says we’re compatible. It’s a lie. We’re clearly not a match.” Grillby rubs his neck. It was hard to stare at Sans like this. “I’m going home.” He turns his back on the two and starts walking without another word. 

He hears Sans call him, but he doesn't turn around. It was better this way. Sans and him really shouldn't have gotten together anyway. This was for the best. 

…


	4. In Love

During the next few weeks of Sans’s recovery, Grillby mostly spent his time away from the skeleton’s home. It seemed like a good idea. Keeping his distance after all the damage he’d done, would put a pin in their relationship. But Sans wasn’t ready to end this with him yet. 

In the middle of the night, against all odds, Sans came to his door wearing a ridiculous outfit. Oversized oven mitts and double layers of sweaters to keep him somewhat insulated. He carried with him a backpack stuffed to the brim that he couldn't even close. Sticking out from the zipper was a fire extinguisher and a tube of lube. 

“LETS MAKE A BABY!” Sans yelled excitedly, pushing his way into Grillby's place. 

Quite shocked, the flame could do nothing but just stand aside as his boyfriend made himself comfortable in his loft. Sans kicked off his shoes and shrugged off the heavy backpack- starting to unpack his supplies right there on the floor. Grillby was confused. He closed his door as a habit so the cool Snowdin wind would not blow inside, but now he second-guessed his decision as he looked at Sans in the double sweater mash. 

He looked like a swollen marshmallow. Grillby might have laughed, if not for how serious his boyfriend was right now. 

Grillby’s home was always kept toasty. It was his place of comfort after all. But with his little guest here he quickly made his way around the living space opening some windows. It would help lower the heat. The home creaked with the swelling of hot and cold air meeting at once. “...I take it Papyrus kicked you out of the house for leaving your socks everywhere again?” Grillby hummed. “I’ll pull out the guest bed for you-” 

“Don’t play stupid Grillbz! You know exactly why I’m here!” Sans stood and tackled the flame in a hug. Grillby had attempted to catch Sans. He wanted to push him away and make sure their distance was maintained, but their mash of limbs inevitably led them to crash on the floor. With Sans on top of him leaning down with a devious smirk. “I’m here so we can have sex.” He blushes brightly, taking the lead to unbutton Grillby’s shirt. 

Grillby winces. A worried look plastered along his brow. “No. Sans…. The reservation isn’t for another month.” Grillby reminds him, with a sigh. He easily pushes Sans from his lap and kneels by his lover. “Besides… after last time… I don't want to hurt you. The last thing I want to do is try this without… doctors around. What if you fall down?!” 

“I wont!” Sans yells. “You wont hurt me.” Sans says softer, those words meant to comfort himself more than Grillby. He stands up to show his lover the things he brought over. 

Sans was prepared to take as many precautions as needed as he got ready for his lover. 

He showed him his mittens from home. The oven gloves weren't as flexible as the ones he had gotten in the labs, but he only needed them to brace himself against the harsher flames. He brought an empty bucket, which he filled with water at Grillby’s sink and placed on the side of the bed. For emergencies. 

Grillby shook his head, humoring him for a minute. “If you’re pinned down and I lose control then who is going to douse us in the water anyway? Sans… I know you don't like the idea of doctors watching us… but it’s a safety measure.” 

Sans sulked, but didn’t give up! 

He was still setting up their love nest. He propped the pillows in such a way that he could be lying down and still have his hips raised at the perfect angle for his partner. It was a slope so… Grillby’s cum could have an extra chance of being potent. Or at least that’s what he read in some undernet post. He also heard that eating lemons before sex makes a monster more fertile… and he wasn’t sure if that was true or not but it was worth a shot! Thats why he ate a whole bunch before he came here. His nerves were on fire. 

Everything had to be perfect. Especially since Grillby was against this whole charade. 

His boyfriend disapprovingly watched with his arms crossed as Sans ran about his home with excitement to get boned. Setting up his own DIY safety measures that looked less secure than what was offered at the breeding facility. 

After such a royal screw up last time they screwed, Grillby was right to be cautious. He didn’t like the idea of trying to shag here. He was excited. But terrified of touching Sans. What if he hurt him again? 

It made the back of his throat burn with anger and regret, but no matter how many times he told Sans that this was a bad idea, his lover was still eagerly preparing a love nest for them. Sans must have been really horny to ignore him.

It seemed no matter what he said, Sans was going to ignore him and try to make this coupling work... so Grillby sighed and sat backwards on a chair. With his arms folded across the back rest he could gaze over the bedroom and watch Sans run back and forth to get things set. He had to close his eyes and try to ignore the other’s hustle. 

Grillby did his own mental preparation. His flames flickered a dim yellow as he tried to reign in his magic. For every single other monster in the underground, their magic was a source of kindness and love. So why did he have to hurt Sans every time they were together? He didn't have the intent to hurt Sans.... none he can think of anyway. Starting a family was just as much his dream as it was Sans's. So they agreed there. 

He dreaded the possibility of his beloved getting hurt if they were close together. But it didn’t deter his lover. There had to be a way the two of them could do this. Without the lab. Was there some way the two of them could…safely… reproduce? 

Didn’t they need a moderator? …Someone to make sure Sans was okay. 

"...Do you want to-?" Grillby's throat closed in on that sentence. He felt like gagging at the mere thought but it had to be said. "D-do you want to ...invite... Papyrus ... over?" Grillby winced. He really shouldn't have. After everything they already had been through, one more pair of eyes watching them be intimate wasn't a big deal anymore. It was ... more important to have Sans healthy. And who else but his brother should be there if he lost his only hit point? Grillby looked outward as Sans was lining the bedspread in plastic wrap. Confusion painting his face. "Sans?" He calls again, louder. "Did you hear me-"

"I heard." Sans nods his head, even though he doesn't give Grillby any eye contact. It really killed the mood to talk about his bro. And what Grillby was implying was far more morbid than what he wanted to think about. 

He sagged his shoulders, staring at his handiwork with the bed and the safeties he'd set up. Though they are silly and largely in the way of a typical romantic bedroom, Sans triumphantly nods his head hoping this rig will work. "I don't want my little bro here. I trust you Grillby. I know you wont hurt me." 

He turns around now and gives Grillby his full attention. Eyelights blown wide with little hearts. A deep haze of ocean mist spread across his cheekbones, as he begins to de-robe. Or... at least de-pants. 

"I want you more than anything else." He wriggles out of his pants, his ecto magic glows brightly. Though neither of them are taking the medication the doctors had recommended, Sans's sex drive is still through the roof. He's been wanting this for years now ever since he and Grillby started dating. "I need you.  _ Please _ ." Oven mitts grab Grillby's hands gently and pulls him out from around the chair and guides him to the bed.

"Sans..." Grillby says with hesitation, but his tone turns to laughter when Sans gets up on the bed, plastic crinkling. "So what the heck is this for." He motions at the wide bed. Sans lies back, all the plastic crinkling beneath him. 

"...If things get too heated, the plastic will burn." Sans says with a wink. Grillby semi nodded- imagining the smell won't be so pleasant that he can ignore it. Then again, the loudspeakers weren't easy to ignore either... but they found a way to work past it. 

He leans down and hovers over Sans, his height dominating the smaller skeleton. "What if I don't stop?"

"I trust you." Sans whispers. Leaning in close. "Besides... I don't want you to stop." He smirks.

He kneads his gloved hand over the front of Grillby's pants. Wanting the Flamester to get as naked as he was so their fun romp could begin. "Won't you be hot in those jackets?" Grillby commented.

"...The magic in clothing prevents them from burning right?" Sans says. "So you can hold me close.... I thought this might be better."

Grillby looks back down at the skeleton splayed out on his bed. He summoned his whole ecto body even though the only the bottom half of exposed flesh was visible. It filled out his clothes and Grillby could feel the softness of it from where he pressed his hands.The pliable form of the chubby skeleton made him gulp. Somehow this was a lot more intimidating than bare bone. 

“Won't I burn you…?” His eyes look venture downward at the organ between their legs. The ecto pussy manifested was a pretty plump flower. Dripping with the morning dew and ready to be pollinated. Grillby gulps. “...Okay… if we’re going to do this… I need you to have a safeword.” 

Sans nods happily, an evil glint in his eyes shines with mischief. “LEGENDARY FART MASTER!” 

His partner is none too enthusiastic about the safeword. In fact. It's a total mood killer. Maybe that was the point. Grillby reluctantly agrees to it. “...fine.” He is happy they have a little safeword. “If I hear that- then… we’ll stop. Okay?”

“okay!” Sans chirps. “One more thing…” He says with a grin. Sans gets to his knees on the bed and bounces around as he tries to shuffle to the lube placed beside the bed. He takes off the oven mits and tucks them under his arm. Eager fingers dive right in and scoop up a glob. 

“...That stuff is flammable.” Grillby shakes his head with worry. “Did you check-” 

“I checked.” Sans scoffs. “...Just let me take over Grillbz. It’s okay.”

His fingers stretch out his small opening. Making lewd squelching noises as the lube worked its way through every crevice of his magic. The muscles there tighten up against the intrusion… and Sans isn’t being that gentle with himself. He knows exactly how much he can take. And if he was being honest, he preferred a little rougher treatment. Everyone thought he was so goddamn fragile… it was gratifying to receive some pleasure in sharp quick thrusts. 

Grillby’s jaw hung open as he watched his lover work himself, open. The show was tantalizing enough that he couldn't pull his sight way from the delicious feast being displayed in front of him. He feels his cock start to stiffen from the sight. He reached out to grab for Sans but- hesitated . 

Images of the other in a hospital gown filled his memory. 

He didn’t want to see sans like that again. 

Nervously he reached a bit higher, aiming for the sweater that hangs off the contours of Sans’s hips. “I love you.” Grillby whispers. The skeleton makes a little sound of surprise. He knows Grillby loves him but those words right now brought little hearts to his eyelight. Conjoined with the motion on his iliac crests... Grillby’s heavy heated hands on his waist made him feel close to the other, even with the layer of clothes as a boundary. 

“I love you too.” Sans huffs a little, a bit embarrassed . “I-I’m ready. You ready?”    
  
Grillby unbuckles his pants, keeping them on since it could be an extra layer of protection between the two. His cock stands high, freed from it's prison. Turned on by everything his little lover did to prepare for this. It only takes a couple quick strokes to get him fully erect. Sans hums out a final exhale of trepidation. He knows how hot it can be to be opened by that pillar of fire. But he lifts his hips up from the bed and angles himself above Grillby. The two rock against each other in small circles. Small moans and sounds slipping past them as their friction increased. 

There wasn’t any audience for them… It was just him and Grillby at long last. Sans felt a sort of power in being alone . Confidence radiated through him as he took more and more control. He wasn’t afraid to let these vulgar sounds slip through his mouth. The only one who would hear them was Grillby.

He wasn’t afraid to let his voice get too loud. 

He grinded his hips down, catching the tip of his heated cock between his wet folds. There was a sizzle between them like bacon on a rainy day. They both shivered at the tingle and anticipation.

With careful small rocking motions Sans slid up and down his shaft. The hot rod parting his lips and smearing the lube across bumpy surfaces. Grillby hitches his breath when his tip finally caught. Just the head entered but there was so much intense pressure that he felt dizzy from entering. 

He was made of fire, but Sans’s inside’s burned hotter. Wrapping him in the heated and moist cavern that was made just for him. Sans made a gurgle in his throat. The beginning of a moan. Such a gratifying feeling of being close to his lover was going to drive him mad if he had to wait any longer. He moved against Grillby, trying to slide his thick cock deeper. 

It split him open with a wet squelch. He made a squeal from the sudden pressure! His eyelights wide with this foreign feeling inside him. Little by little he was able to rock down more and more until he was finally seated all the way on top of Grillby. A little sweat stuck to his clothes and Grillby’s hands grabbed at his sweater, wanting some place to hold. “Still good, Sans?”

“F-Feels good.” Sans’s tongue hung out as he panted. From half lidded eyes, Sans sultrily looks down at the monster below him. “I can’t wait… for you to… fill me with your cum.” He groaned, pushing his knees off the bed to lift himself and sit back down on his throne. Speared on Grillby’s dick he moved up and down with soft pants for air. His breath was making small pants in the room. 

His freshly stretched out pussy clenched tightly. He could feel the pulse of Grillby through where they were connected. A burn at the base of his pelvis. 

Sans closed his eyes and bobbed back and forth. Eliciting a disgruntled sound from Grillby. Caught off guard. They continued rocking back and forth. Shallow thrusts, turning frantic as he adjusted to the girth and sped up. 

“Sans…”Grillby moaned. With his head on the pillows, his eyes white hot coals. “...nn...stop. I can’t control myself around you.” His mouth parted, to produce billows of smoke. He was trying to redirect his heat inward like an oven. Sans coughed a bit, raising the neck of his sweater over his nasal cavity. 

“No. I… we..” he let out a cough again. Trying to make it seem like he was just clearing his throat.This was so much different than the iced chamber they were in before. The room swelled with heat. “We can do this. I need you. Please Grillby. Dont quit.” 

He sat back on his knees. Loving the feeling of being filled all the way. Grillby’s length poked out the front of his ecto stomach. Large enough to cause a small bump inside. Sans raised his sweater to show off. Poking his tummy, and eliciting a sexy growl from Grillby as his member felt the touch too. 

His ecto magic revealed everything. And Grillby sat back in awe of the blistering ecto magic boiling around him. It was like Sans’s magic was rippling and reforming to take him all. It swirled around in a beautiful haze of color. Sans was dripping sweat. Every curve of his ecto body was hot and sticky from the excessive clothes. 

“Look how deep you are…” Sans moaned. One hand pressed against the curve in his ecto stomach. And he fingered himself while he sat back, stretching a phalange over top Grillby’s dick and inside him. The added intrusion sends a tremor through both of them. 

“Please…” Sans begs. His insides squeeze tightly. The walls of his magic pulsing as Sans purposefully clenches his muscles over the cock. His eyes roll back in his skull with a moan and hi tongue hangs out his mouth. The sweet burn inside was devouring him. Sweat drips off his chin. “Please finish inside me. I want it. I need it.” 

Grillby gulps, it stirs his embers to see Sans wanton like this. He fleetingly grips one of Sans’s legs to pull forward and lock him in place. He grabbed Sans’s hands next, forcing the oven mits to hold his own legs down before Grillby gave a brutal thrust up into that tight heat. It made the skeleton see stars and gasp as Grillby slammed into him from below. 

Pressed together like this, each jerk dug deep into his insides. Grillby growled as he got a look at Sans’s bulging exto stomach. He could see himself already breaching into that tiny pocket of a womb. Every thrust had Sans crying in pleasure as he bounced on his cock. 

“Grill-!! Oh!! Th-there!! That- feels!!!” Sans gasped and lolled his head out to the ceiling, pleading with the sun and stars to let him climax. His clit was bopped every time he slid down and his womb was opening up to allow Grillby in further. The press was painful but so much pleasure and pain was already mixing in from their joining. “I want it. .I wanna fe-feel you cum inside!” His scream drove Grillby to thrust in a final time before his hot magic was flooding that empty baby room. 

Sans screamed. Still clenching down on Grillby when he spasmed and came too. His cunt milking Grillby for every last drop. “Shhhit.” Grillby slurred, orgasmic bliss was rocking him through the overstimulation. His sweet pussy was drawing everything from him and Grillby was still rocking into that tight space. 

His eyes widened when he saw Sans’s magic ripple and stretch to hold more. His thick fiery red cum was staining the inside of the blue magic. It swirled together to form a new color in the spectrum of purple. The only thing holding it in was Grillby’s cock still throbbing deep inside. Cum dribbling out, at the sight of seeing Sans so beautifully wrecked. The skeleton mewled as the two came down from their high. 

Sans’s thighs and pussy were scorching. Raw from the contact with his love. 

Sans was shaking. Tears dripping from the side of his sockets. “M-more.” He begged. His whole body convulsed as his sensitive pussy slid up against Grillby. Cum splattering their thighs as the only plug filling him was removed. “You… you need to breed me properly.” Sans begged. His eyelight blown wide as he slid against Grillby again. Trying to work him up for a second round. 

Grillby let out a shaky breath. He pulled Sans up away from him. Hearing his love scream as his cunt gaped at the emptiness inside him. Cum dripping freely from the loose opening. But it wouldn't be for long. He flipped them over, setting Sans down on the pillows and towered over him. He sheathed himself back inside that warm cunt a moment later. Hovering over Sans with a devilish smirk. “I’ll fill you again and again until your belly is bursting.” He rubs a soothing palm over Sans’s stomach. 

The night is filled with endless screaming and moans as the two frick on into the early daylight hours. They weren’t holding anything back. They weren’t going to let their chance go to waste.

Nearly all the underground could hear their throes of pleasure, -since all the windows were open. It was lucky it was so late at night that it wouldn’t catch the attention of anyone. Sans cried as Grillby pushed him into different arrangements. Thrusting up into him while his legs were over his shoulders and pinned to the bed and sideways and snug around his waist. They did it on the bed. The wall. The floor. Sans grabbed Grillby by the shoulders and hung on for dear life as he was smashed into oblivion and still- desperate for more.

And finally… finally when their feverish need was over… the blissful night of sex gone. And the morning of the underground lights filtering in through the windows-... Sans and Grillby sat on bed with a satisfied and exhausted goofy look on their face. 

Grillby was the first to get up. He went straight to the freezer to grab anything he could with a pair of tongs and held it out for Sans. His love weeped with a giggle. Face temporarily warped into an open ‘o’ as he recovered what little breath he could. 

He took the bag of peas and shoved them between his pelvic inlet. Not caring that Grillby and his mixed fluids were discoloring the label. The ice cold bag felt like instant relief to the firey burns at his pelvis. 

Grillby knelt between them, trying to apply burn cream to his thighs and hips. His bones were charred painfully… though the burn was an instant sealer to any wounds that opened up during sex. Grillby apologized with a squirt of gel applied to each of these parts. Sans mewed in his throat. The rough fucking had his mind in other places. He lied back in bed and let Grillby do whatever he wanted with him. He felt so full. His ecto magic was holding in everything Grillby gave him. 

“Still with me Sans?” Grillby soothed healing magic over his bones. Not that it would help much. 

“M-more…” Sans moans as he’s done for the past hours. Grillby chuckles in his throat. 

“I'm cutting you off.” He smirks, reciting the line as he had done in his bar many times. “You’ve had more than enough.” He leans in to kiss the swollen ecto bump at Sans’s stomach. “It’s not going anywhere… your magic is starting to process it.” He rubs the bump, making Sans shiver at the newfound stretch in magic. 

“G-good.” Sans whispers. “I… I want it all. I wanna have your kids.” Sans rubs up against the frozen vegetable bag. Rolling his hips into the icy relief. 

Grillby smiled, pitying his thoroughly fucked partner. He couldn't even sit up right yet all Sans was doing was convulsing and moaning. Trying to fuck into the bag of peas like it was a pillow to hump. Grillby patted it down, easing San’s hands to calm. And dragging him back to a place of sanity. “Shh.. Sans… no more.” 

Sans presses the bag tight to his bones. “Ow..”

“...Sorry.” Grillby wilts.

“...hurtsss.sss..so good.” Sans closes his eyes, pinching the bag of peas to his pelvis. “Cold… good.” He sounds exhausted. He falls back down on the pillow and his breaths become a little less quieter. His recovery needed some sleep. Grillby wants to sleep too. 

But he does the best aftercare he can first, literally caring for every bone and burn that he can see. And after, even wriggles fingers past Sans’s tight ring of muscles in his pussy and spreads the anti burn cream there too. Bandaged him up and tucked him in bed. 

When Sans started to look like a mummy in anti burn gel and bandages.. Grillby was sure that he had reached every spot. Being over protective to the point where he didn’t even let the slightest freckle out of his sight. He didn’t want Sans to burn up again like last time. Better to patch excessively than not at all. He laid a kiss on his cheek. And Sans’s fuzzy eyelights focussed on him. 

“m-more?” Sans opened his mouth. Blue tongue asking for a kiss. Grillby is reluctant at first… but after all the banging they've done, one small kiss wouldn't hurt. 

He leans forward and claims Sans’s mouth. He means for a small peck on the teeth, but the blue tongue presses into his red tongue and Grillby’s eyes bloom open wide. They deepen the kiss. Sans pants hotly as his mouth is wet and sizzles at the contact. 

Sans giggles pulling away with a satisfied grin. “...that's the first time you’ve kissed me.” He whispers. Grillby turns hysteric. He giggles too. His small chuckle turns into a deep laugh. They’ve never so much as held hands before or kissed… and now… they just had spent the most amazing night with each other. 

It was a dream come true. 

**Notes for the Chapter:**

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> Did I leave out a tag? Let me know!   
> Thanks for reading! If you enjoyed please share it around! ('w')b


	5. Bonus pic

^o^)/ I forgot some people might not see my twitter. So here's the final pic of these two.  
They get two baby bones out of all the mindless fracking~ yay~! ♥  
  


**Author's Note:**

> Thank you for reading lovelies! ♫-(^w^) I write and do comics too you can find me here:  
> [My NSFW Twitter (18+only)](https://twitter.com/JellyFicsnFucks) and [ My Pillowfort♥ ](https://www.pillowfort.social/Jellyficsnfucks)


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